1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus, and more particular, to a substrate processing method for processing a substrate formed with a thermally-oxidized film and a silicon nitride film.
2. Description of the Related Art
A semiconductor device wafer (substrate) has been known that has a thermally-oxidized film, such as an oxide silicon film, formed by thermal oxidation processing and a silicon nitride film formed by CVD processing or the like. The silicon nitride film is used as an antireflection (BARC) film or a spacer for separating a gate from a source/drain. The thermally-oxidized film constitutes a gate oxide film.
A method of etching a silicon nitride film has been known (see Japanese Laid-open Patent Publication No. 2003-264183), in which a compound gas that contains fluorine as a constituent element and does not contain carbon as a constituent element, such as for example a compound gas containing HF gas, is converted into a plasma, and the plasmarized compound gas is reacted with carbon to produce chemical species (radicals) by which a silicon nitride film is etched.
However, even the thermally-oxidized film is etched by the chemical species. For example, in the case of a wafer having a silicon substrate on which an oxide silicon film (thermally-oxidized film) is formed as a gate insulation film and a silicon nitride film as an antireflection film is further formed on the oxide silicon film, not only the silicon nitride film but also the oxide silicon film is etched by the above described etching method. Since the gate insulation film is usually formed to be thinner than the antireflection film, the oxide silicon film is removed prior to removal of the silicon nitride film. As a result, even the silicon substrate is impaired (etched).